$\begingroup$They are overwhelmingly masked by plate tectonics. The slow contraction of the Earth is essentially taken up by ductile deformation in the mantle and by the movement of tectonic plates.$\endgroup$
– bonFeb 8 '17 at 21:37

2

$\begingroup$@bon sounds right. Also, Earth's core is much larger so it cools slowly, and it's also better insulated so I guess that makes cooling also slower. Note that most of Mercury's volume is taken up by the core, whereas it's not for the Earth. I guess this also has something to do with why doesn't show up on Earth.$\endgroup$
– GimelistFeb 8 '17 at 23:07

$\begingroup$Sounds like good information you guys give. Fleshing it out into a complete answer would be great!$\endgroup$
– JeopardyTempestFeb 11 '17 at 8:30